Process for the treatment of marmatitic zinc ores



Feb. 3, 1948. N. c. CHRISTENSEN v 2,435,340

PROCESS FOR THE TREATMENT OF MARMATITIC.ZINC ORES 4 Filed May 1, 1.944

ORE

, Of CONCENTRATE SULPHATOR HZS 1 50x Reiurn' LEACHING WOSh solufion 4 FILTER iquhngs \o f Pb recovery 5 I FILTER plan so 0 0C n g soiufion e 4 A i X7 6 .acd

EVAPORATOIR 6 o a 985% H250 g I 0'' EVAPORATOR ZnSO crysiqls FILTER and diluh acid I u FLASH WASHER soluHn J j 1' a wash wafer ELECTR LYTE 5 o k r r CELLS ii=i l 9 SO3ABSORBER DECOMPOSER 8 preclpl u e iron oxide Oder Z m l FILTER 2 5? FILTER mssowmcs solufion "W TANK LEACHING AGITATOR Patented Feb. 3, 1948 PROCESS FOR THE TREATMENT OF MARMATITIC ZINC ORES Niels C. Christensen, Salt Lake City, Utah, as:-

signor to Combined Metals Reduction Company, Salt Lake City, Utah, a, corporation of Utah Application May 1, 1944, Serial No. 533,633

Claims. 1 This invention relates to the treatment of zinc sulphide concentrates in which the zinc mineral contains relatively large percentages of FeS i. e. ores in which the zinc mineral is marmatite or contains suflicient' F'eS to be classed as marmatitic. The treatment of such ores by ordinary electrolytic methods in which the concentrates are roasted and leached with H2SO4 and the solution is electrolyzed for the recovery of the zinc is diflicult or-uneconomic due to the formation of anexcessive amount of zinc ferrite in the roasting operation and the dissolving of an excessive amount of iron in the leaching operation. By the process of this invention the difliculties of the roasting operation is eliminated and the iron is eliminated from solution without the difficult and cumbersome precipitation and washing step required in the commonly used electrolytic process of zinc-recovery. In the process of this invention the zinc sulphide concentrates are leached with sulphuric acid in their natural state and the dissolved iron is separated from the ZnSO4 by acalcining and leaching operation in which the iron is changed to ferric oxide and the S03 is recov-' ered for use in the process and'the pure zinc sulphate is electrolyzed in a relatively strong acid electrolyte of substantially constant composition. The accompanying flow sheetillustrates the method of carrying out the process which is set forth in detail in the following description.

The Zinc concentrates a are ground with an excess of sulphuric acid of approximately 60% concentration in a sileX lined pebble mill 1 (marked sulphator on the flow sheet) to convert the lead and zinc sulphides to'sulphate's. As fully set forth in my U. S. Patents Nos. 1,434,084 and 1 ,937,633 hot sulphuric acid at a concentration of approximately 60% H2802 acts upon the ZnS to form ZnSOr andHzS as indicated in the follow-- ing chemical equation:

ZnS+HzSO4=ZnSO4+H2S As also fully set forthin the above-mentioned patents, the solubility of ZnSO4 in H2804 is at a minimum in sulphuric acid containing in the neighborhood of 60% H2SO4, and it is therefore necessary to subject the mixture-of concentrates and hot acid to grinding or attrition to remove the-coating of ZnSOr from the'zinc sulphidepartitles and permit the-reaction to go to completion and, convert all the ZnS to ZnSOr. The FeS in the zinc mineral is also converted to FeSOr by this treatment and as the solubility of the FeSO4 is also at a minimum in sulphuric acid and of a concentration in the neighborhood of H2804, the grinding operation in the sulphator l results in the conversion of both the ZnS and FeS to solid ZnSO4 and FESO'4. The galena in the ore is also converted to PbSO4 in the same manner. The pyrite in the ore, as also set forth in the above mentioned patents, is not acted upon by acid of a concentration in the neighborhood of 60% H2804. Sufficient excess hot acid is used in the grinding operation to form a fluid pulp and to prevent the lowering of the concentration of the H2SO4 in the acid below the point at which the acid acts upon the zinc sulphide mineral. With most ores of the marmatitic type a treatment period of one half hour is sufiicient to convert substantially all the 211s and FeS in the zinc mineral to ZnSOr and FeSOr. To prevent low ering ofthe H2804 concentration in the sulphating operation below the point at which the acid does not act effectively upon the zinc sulphide mineral, the concentration of the incoming acid is made sufilciently above 60% to take care of the acid lost in the formation of the sulphates in the sulphating operation;

The mixture of ore residue and solid sulphates b is separated from the excess or circulating acid 0 on the filter 2 part of the excess acid 01 being passed through the heater 3 and returned to the s'ulphator I for use in" treating more zinc concentrate and the remainder ofthe excess acid .6 being sent to the evaporator B, and the mixture of ore residue and solid sulphates and residual acid b ismixed with-sufficient hot'wa'sh solution from the filter 5 to dissolve the ZnSO4 and FeSO4 in the acid solution and form a hot concentrated sulphate solution. The ore residue f containing the Au and silver sulphide and PbSO4 is separated from the acid sulphate solution 9 and Washed with hot water on the filter 5; the ore residue and PbSO4, Ag2S and Au being sent to the lead smelter or lead leaching plant for recovery of the Pb and Au and Ag, while the acid ZriSOr-FeSO; solution 9 is mixed with circulating acid efrom the filter 2 and concentrated in the evaporator 6 to bring the acid concentration to approximately 60% H250; and thus precipitate the greater part of 3 V theZn804 and R804 from the solution. (surficient circulating acid e is added to the acid Zn8O4 solution 9 to carry the precipitated Zn804 and FeS04 crystals in suspension in the evaporator, and the hot wash solution 9 is used to form H2804 with the S03 from the decomposer 8 as later described.) The mixture of solid Zn804 and Fe804 h is separated from the concentrated sulphuric acid solution i (approximately 60% H2804) on the filter I and the greater part of the H2804 is washed out of thefilter cake of mixed sulphate crystal by a flash wash with water, the wash solution ;i being used to make H2804 from the 803 supplied to the absorber 9 from the de-' Q I composing furnace 8 (indicated as decomposer.

decompose the Fe804 to secure sea and ferric oxide as indicated in the following hemical equa- The decomposition is carried out in a multiple hearth muflle type furna'cefthe mixed sulphates 1 treating more zinc concentrates.

1 Irecoveredior reuse-in the process with the ex-' .ception of the relatively small amount of loss in remove the amount of acid generated'by decom- 60% H2804 and thus precipitate the zinc as Zn804. The crystalsof Zn804 z. are separated from the H2804 on the filter II, the crystals and adhering acid being returned to the dissolving and mixing tank I4 and the approximately 60% acid a: being sent to the sulphator I for use in The acid concentration in the electrolytic circuitisrnaintained at the maximum which is possible for efficient operation so as to keep the amount of evaporation requiredin the evaporator It at the min- 1mum.: mm;

" By the process described above, the sulphuric acid required in the process is regenerated and the form of 802-made in the decomposition of theFeS04. This loss must be made up by supand residual H2804 being fed. to the top hearth and passed downward throughsuccessive hearths in counter-current to the air which is passed upward'through the furnace, theupper hearth being maintained at a temperature of approximately 400 C. and the temperature increasing successively on lower hearths to approximately 600 C. on the lowest hearth. In the passage of the mixed sulphates through the decomposing furnace the Fe804 iscompletely decomposed whereas the Zn8O4 is not afiected. The 803 k gases from the decomposing furnace 8 are ab-' sorbed in the spray absorber 9 in the concentrated circulating acid 1, the wash "solution 4 from the filter I being added to the circulating acid at successive points of solution vflow in'the absorberso as to maintain the acid concentration in the absorber at substantially 98.5% H2804. The concentrated H2804 from "the absorber 9 is-mixed with the 60% acid 1' and returned to thesulphator I for use in sulphating the'concentrates.

I The mixture of ZnSO4and-Fe2Oa m is leached with hot wash solution" from the filter I I in the leaching agitator II) to dissolve the'Zn8O4 and form a hot concentrated-Zn804 solution. The Fe203 o is separated from the hot concentrated Zn804 solution 11 on the filter I Iiand washed with water, the wash solution being sent to the leaching agitator I 0 and the hot saturated Zn804 solution n is treated with zinc dust in the Cd pre-- cipitator I2 to precipitate the Cd (and the other impurities such as Cu and 'Ag) from solution. The Cd precipitate p is separated from the Zn804 solution in thefilter I3 and th purified Zn8O4 solution q is mixed with Zn804 crystals from the .filter I1 and return solution it from the electrolytic cells I5 in the mixing tank I4 and this mixed electrolytes is electrolyzed in the electrolytic cells I5 to recover the zinc as metal and regenerate the H2804. The electrolyte in the cell circuit is maintained at the desired acid and zinc concentration by rapidly and-continuously circulatingthe electrolyte through the cells, through the mixing tank I 4 and back through the cells as indicated on the flow sheet, the electrolyte being cooled to the desired temperature in the mixing and; dissolving tank I4 in each circulating cycle. From this circulating electrolyte t suiplying this amount of acid to the leaching operat'iorf. The process as described makes it possible to treat th marn'iatitic zinc ores without roasting, recovers the sulphuras H28 which may be utilized as such or-from which the sulphur may be recovered as metallic. sulphur, and allows the recovery of the zinc as metal by electrolysis in aihigh acid electrolyte of substantially constant conditions especially favorable to efiicient operation. I

What is claimed is: v r j 1.- The process of treating marmatitic 'zinc sillphide ores and concentrates which consists in grinding said ores or concentrates with-an excess of hot sulphuric acid containing in the neighborhood of 60% H28O4-so as to convert the Zn8 and Fe8 in the zinc mineral in said ores or concen the sulphur asI-I28, separating the excesstacid from the solid sulphates and ore residue and using said excess'acid inthe treatmentof more ore or concentrate, leaching said mixture of ore residue and solid sulphates-with hot watertc forma concentrated solution of sulphates, separating saidsulphate solution from the ore resi-, due, adding H2804 in sumcient amount-to. carry in suspension th solid sulphates-formed in the subsequent concentrating operation, evap.- crating said last solution to bringthe acid con; centration therein to approximately 60% H2804 so as to precipitate Zn80' and F6804 from said acid solution, separating the precipitated sulphate crystals from the concentrated acidand hot'water to form a concentrated Zn8O4 solue tion, separating the FezOa from the" 211804 solu-; tion, treating the hot Zn804 solution with Zn to precipitate metals below zinc in the electromotive series, separating the 'precipitatedmetals from said solution, mixing the purified Zn804 solution with sulfuric acid electrolyte froman electrolytic cell and with precipitated Zn804 crys-i tals to form an electrolytic solution, electrolyz: ing the latter in the aforementioned electrolytic cell jto recover zinc therefrom'and form "H280 ficient electrolyte u is continuously withdrawn to insol ltion, removing a portion of the .ele'ctrolyze'd solution, concentrating said portion to raise the concentration of acid therein to approximately 60% H2804 and thereby precipitate th ZnSO; crystals therefrom, separating the ZnSO-r crystals from said concentrated acid, using said concentrated acid in treating more ore or concentrate as described, and using said separated ZI1S0& crystals together with another portion of the electrolyzed solution for mixing with more purified Zn804s'olution to form an additional quantity of electrolytic solution for electrolysis.

2. The process for treating marmatitic zinc sulphide ores and concentrates for th recovery of the zinc therefrom which consists, in grinding said ores and concentrates with an excess of hot sulphuric acid containing in the neighborhood of 60% H2804 so as to convert the ZnS and FeS in the zinc mineral in said ores or concentrates to solid Zn804 and R804 and drive off the sulphur as H28, separating the excess acid from said solid sulphates and ore residue and using said acid in the treatment of more ore or concentrate, leaching said mixture of ore residue and-sulphates with hot wash solution from the subsequent filtering and washing operation to form a concentrated sulphate solution, mixing said solution with 60% H2804 in sufficient amount to carry in suspension the solid sulphates precipitated in the subsequent concentrating operation, evaporating said last solution to bring th acid concentration therein to approximately 60% H2804 so as to precipitate Zn804 and Fe804 from said acid solution, separating the precipitated sulphate crystals from the concentrated acid and flash washing the filter cake of said crystals with water to remove the greater part of the residual H2804, using said concentrated acid to treat more ore or concentrate, and using said wash solution in the absorption of 802 from the decomposition of Fe80i as described below, heating the mixture of crystals of Zn8O4 and Fe804 in the presence of oxygen to drive of! the residual H2804 and decompose the Fe8O4 to form FezOa and 803, absorbing said 80: in the presence of said wash solution to form concentrated H280; and using said acid in the treatment of more ore or concentrate, leaching the mixture of Fe202 and ZnS04 from said decomposing operation with wash solution from the subsequent filtering and washing operation to form a hot concentrated Zn804 solution, separating the F8203 from the hot ZnSOr solution and washing the Fe203 with hot water and using the wash solution in leaching more Fe20s-ZnSO4 mixture as described, treating the hot Zn804 solution with zinc to precipitate metals below zinc in the electromotive series and separating the precipitated metals from said solution, mixing said solution with sulfuric acid electrolyte from an electrolytic cell and with precipitated ZnSOr crystals to form an electrolytic solution, electrolyzing the latter in the aforementioned electrolytic cell to recover zinc therefrom and form H2804 in solution, removing a portion of the electrolyzed solution, concentrating said portion to raise the concentration of acid therein to approximately 60% H2804 and thereby precipitate the 211804 crystals therefrom, separating the Zn80'4 crystals from said concentrated acid, using said concentrated acid in treating more ore or concentrate as described, and using said separated ZnSO; crystals together with another portion of the electrolyzed solution for mixing with more purified ZnS04 solution to form an additional quantity of electrolytic solution for electrolysis.

3, In the treatment of marmatitic zinc s'ulphide ores or concentrates the steps which consist in, grinding the said ores or concentrates in their chemically unchanged state with an excess of hot sulphuric, acid containing in the neighborhood of 60% H2804, thereby converting the 2:18 and Fe8 in the zinc material in said ores or concentrates to solid Zn804 and Fe804 and driving oil the sulphur as H28, separating the excess acid from the solid sulphates and ore residue and using said acid in the treatment of more ore or concentrate, leaching the mixture of ore residue and solid sulphates with hot water to form a concentrated sulphate solution, adding H2804 to said solution and concentrating the acid solution to bring the acid concentration to approximately 60% H2804 and thereby precipitate the Zn8O4 and Fe804 from the acid solution, separating said sulphate crystals from said acid and using said acid in the treatment of more ore or concentrate, calcining said mixture of sulphate crystals in the presence of oxygen at a temperatur below the temperature of decomposition of the Zn804 to decompose the Fe8O4 and form iron oxide and S03 and leave the zinc in the form of sulphate, absorbing said 803 in a concentrated H2804 solution to form more H2804, using said last H280; in treating more ore or concentrate and leaching said mixture of iron oxide and Zn-SO-i with water to form a concentrated ZIISO4 solution and separating said solution from the iron oxide.

4. In the treatment of marmatitic zinc sulphide ores or concentrates the steps which consist in, grinding the said ores or concentrates with an excess of hot sulphuric acid containing in the neighborhood of 60% H2804, thereby converting the ZnS and FeS in the zinc material in said ores or concentrates to solid Z'nS04 and Fe804 and driving ofi the sulphur as H28, sep arating the excess acid from the solid sulphates and ore residue and using said acid in the treatment of more ore or concentrate, leaching the mixture of ore residue and solid sulphates with hot water to form a concentrated sulphate solution, adding H280; to said solution and concentrating th acid solution to bring the acid concentration to approximately 60% H280; and thereby precipitate the Zn-8 O4 and Fe804 from the acid solution, separating said sulphate crystals from said acid and using said acid in the treatment of more ore or concentrate, calcining said mixture of sulphate crystals in the presence of oxygen at a temperature below the temperature of decomposition of the Zn804 to decompose the Fe804 and form iron oxide and a and leave the zinc in the form of sulphate and absorbing said 803 in a concentrated H2804 solution to form more H2804, using said last H2804 in treating more ore or concentrate, leaching said mixture of iron oxide and Zn804 with water to form a concentrated Zn804 solution, separating said solution from the iron oxide, purifying said Zn 804 solution and electrolyzing the pure Zn804 solution to recover the zinc therefrom and form H2804, concentrating electrolyte containing said H2804 to approximately 60% H2804 to precipitate the Zn80-4 therefrom and separating the Zn804 crystals from said acid, using said acid in the treatment of more ore concentrate, and returning the Zn804 crystals to th electrolytic circuit with more purified Zn804 solution for electrolysis. Y

5. A process according to claim 3 in which the concentrated ZnS04 solution is electrolyzed in a relatively strong acid electrolyte of substantially constant composition to recover zinc as metal and Number Name I Date regenerate the H2804 to treat more ore or oon- 880,775 De Bechi Mar. 3, 1908 centrat-e. 7 ;914,649 Evans ...;Mar. 9, 19709 NIELS C. CHRISTENSEN. 1,779,841 Fischer 0012.28, 1930 r I 5 1,937,633 Christensen Dec.'5, 1933 REFERENCES CITED 2,001,409 Christensen May 14,: 1935 The following references are of i'ecord in the 2,007,233 Wespy -.---vy 1935 file of this patent: x OTHER REFERENCES UNIIED STATES PAIENIS Lunge, Sulphuric Acid and Alkali, fourth I Number Name Date edition, vol. 1, part3, page 1338. Gurne'y'anq 203,849 Parnell May 21, 1878 Jackson, London, (1913). 

